Purification of low melting point alloys



1945- v A. B; RICHARDS ETAL 2,391,516

PURIFICATION OF LOW MELTING POINT ALLOYS Filed June 16, 1943 Q N I g V ll In I ""3 w I l g l l hum ul u 1 l H HUL I I I ILi I L iXWiSHIE Q %\3QQQ\ I A.B.R1'cL ard .s J. T. o'Rfl-ll INVENTOR.

Maw c/ Z Patented Dec. 25, 1 945 PURIFICATION OF LOW MELTING' POINT ALLOYS Alvin B. Richards and James OReilly,"Dearborn, Mich, assignors tO-FOI'II Motor Company, Dearborn, Mich., a corporation of Delaware:

Application June 16, imasmamo. 490,978

2 Glaims.

This invention relates to the salvage treatment of low melting point metal alloys and, more particularly, to a method of purification of such alloys for re-use in tube-bending operation.v

The principal advantage of this invention is ('Cli 266 -934") a and hydroxide formed. varies that it furnishes a means by which low melting point alloys of the general Woods metal type,

which are commercially known as Cerro-bend and under other. proprietary names or trademarks, may be salvaged, purified, and. made availablefor continuous re-use intube-bending operations. In this work-,tubesof aluminum or other metals used inaircraftconstruction, are

filled with. fluid metal which, because. of. its low melting. point, does not adversely afiect the tube structure itself. The alloy is allowed to solidify in place and then the composite tube and its alloy filling are. bent by automatic bending machines or other means to the precise alignmentand configuration required. The use or the alloy filler, of course, permits the bending operation to be carried out without buckling. or extreme deformation. of. the pipe from the desired circular cross section. After the conformation isobtained, the alloy filling is melted out by placing. the tube in from- 5.6 to 9.0, it, is apparent: that these lighter impurities as well as most of the salts and the dirt described in the Classes 1, 2 and 4- above may be removed by gravity separation. However, the heavier hydroxides and the dissolved. materials require chemical treatment for removal.) While means of attacking this problem are-available to labora- .tOIy or research chemists, the purpose of the present invention is to devise a method which is substantially automatic and requires no particular skill or maintenance in its operation, yet which will yield: a. continuous supply or purified Woods metal for re-use in the tube-bending process, 1 The practical advantage is at once apparent when it is considered that the alloy sells at approximately $.75 per pound and, particularly at the present,ineorporates strategic materialssuch as tinand.- cadmium which must be conserved at all costs. At the same time, atypical pipe bending installation may produce upwardly of 10,000

hot water, which filling may be salvaged for reuse, While the term Woods metal is used herein, it will be understood that equivalent alloyshaving substantially a bismuth, tin, lead and cadmium content and characterized by a low melting. pointv are comprehended within its terms.

However, successive re-use of the alloy builds upits. impurity content and in time it becomes socontaminated with oxide, slag, debris, etc., as to be unusable for the purpose described. These impurities, investigation has shown, include:

1-.-Salts deposited by the water which evaporated in the filling and melting-out tanks.

2. Oxides and hydroxides of the metals making up the alloys,

3. Small amounts of dissolved aluminum.

4. Dirt introduced by allowing the metal to spill on the floor-during some stage of the process.

While these included impurities have considerable effect upon the characteristics of the alloy in use, they actually constitute a very small per centage of the total volume of the metal. As

Woods metal with its composition of:

Per cent Bismuth 50 Lead -Q. 25 Cadmium 12 /2 Tin 12 is rather heavy, having a specific gravity of about 10.7, and the specific gravity of the various oxides pounds of the contaminated metal per month. Heretofore, this metal has been unavailable for further use and represented a substantial loss unless: it were subjected. to a precisely controlled reconstituting technique. The apparatus disclosed and. the method of its operation permit the economical salvage. of the metal without deterioration in quality or diminution in quantity and by means which are safe in operation, economical in structure, and practically automatic in operation.

With these and. other objects in view, the invention consists in the arrangement, construction and combinationoi the various partsof the improved device, described in the specification, claimed in the claims, and illustrated in the accompanying drawing in which:

Figure 1 is a vertical transverse sectional view through a purification plane setup.

Referring to the drawing, a gravityseparating device is indicated generally at I10, an acid-treat- I ing tank at II, neutralizing bath at I2 and pigging molds at I3. The gravity separator includes a tank [4 to which molten impure Woods metal is supplied through the pipe l5, controlled by the valve Hi. This tank, as is each of the others, is provided with a water jacket I! to maintain the temperature of the alloy above degrees Fahrenheit, so that it will remain molten at all stages in the operation. After introduction of the molten impure alloy to the tank M, the lighter components, as described heretofore, separate in the form of a slag l8'which may be drawn off at operated without technical control.

26 into the rubber-lined tank 21 which is again water jacketed at 28 and heated by steampipes 29. This tank contains a hydrochloric acid solution which, for best results, should be maintained at about per cent hydrochloric acid by volume or 8 per cent by weight.

Since the alloy is in the form of small droplets and is intimately mixed in transit through the bath 30 by passing over bafiies 3|, the heavier oxides, etc., and the dissolved materials are subcipitates them in the form of a sludge which eventually builds up on the bottom of the tank. However, as the amount of these impurities is relatively small, the sludge forms very slowly" necessary to use the metal to its practical exhaustion point which meant that as it was reused, its affecting metal point varied and its homogeneity decreased. Using the present apparatus, it is perfectly feasible to purify the metal at frequent intervals with consequent improvement in its working quality.

Some changes may be made in the arrangement, construction and combination of the various parts of the improved device without departing from the spirit of the invention, and it "is the intention to cover by the claims such jected to the hydrochloric acid which pre- 20 and it is only necessary to remove it at infrequent 5 intervals. The alloy continues on its course as shown and finally collects in a sump 32 from which it is withdrawn by the pipe 33 controlled by. the valve 34 and again discharged in the form tralizing bath I2.

The neutralizing bath l2 again includes a waof droplets 35, the trough 36 leading to the neu- 30 ter-jacketed tank 31 containing a weak sodium I bicarbonate or equivalent alkaline solution which washes and neutralizes the metal droplets entering. it. These build up into a considerable amount of purified alloy 38 at the bottom of the tank which may be withdrawn through the pipe 39 controlled by the valve 40 and poured into the pigging mold l cakes.

It will be noted that the apparatus devised in 3 for solidification into individual this operation is extremely compact and may be Indeed, it

will be found that it may be operated substanchanges as may be reasonably included within the, scope thereof.

The invention claimed is:

1. In an apparatus for the purification of used Woods metal and similar low melting point alloys, a settling tank to hold impure molten alloy, means to maintain the temperature of said tank above the melting point of said alloy, means on said tank to remove the lighter separable portion of the charge therefrom, means to discharge the heavier remainder of said alloy from said tank in the form of minute droplets and to direct said droplets into a second tank containing an acidic solution, means to maintain the temperature of said second tank above the melting point of said alloy, means on said second tank to discharge the accumulated alloy therefrom in the form of minute droplets to a third tank containing a neutralizing bath, means to maintain the temperature of said neutralizing bath above the melting point of said metal, and means to withdraw the metal from said neutralizing bath.

2. In an apparatus for the purification of used Woods metal and similar low melting point alloys, a settling tank designed to receive said impure molten alloy, means to maintain the temperature within said tank above the melting point of said alloy, means to withdraw the lighter portion of said charge from said tank, gravity means in communication with said tank to discharge the heavier portion of the charge therefrom in the form of minute droplets and to convey said droplets to a second tank containing an 

